Inspection device, inspection system, and inspection method

ABSTRACT

An inspection device ( 1 ) inspects an amount of dielectric particles contained in a sample liquid. The inspection device includes a dielectric collection unit ( 3 ), a pump unit ( 10 ) and an AC voltage supply unit ( 11 ). The dielectric collection unit includes at least one pair of electrodes ( 41, 42 ) and a flow channel ( 13 ) extending in a predetermined direction on the pair of electrodes. The pump unit is configured to feed the sample liquid to follow the flow channel in the predetermined direction. The AC voltage supply unit is configured to supply, to the pair of electrodes, an AC voltage with a predetermined frequency to cause dielectrophoresis for dielectric particles in the fed sample liquid. The dielectric collection unit includes a plurality of slit regions (Rs) aligned in the predetermined direction between the pair of electrodes. Each of the plurality of slit regions is separated from each other within the flow channel.

TECHNICAL FIELD

The present invention relates to an inspection device, an inspectionsystem, and an inspection method for inspecting dielectric particlessuch as bacteria and cells in a sample liquid.

BACKGROUND ART

An inspection method by using dielectrophoresis is known as inspectingdielectric particles such as bacteria and cells contained in a sampleliquid.

For example, Patent Literature 1 discloses a microorganism detectionmethod for the purpose of efficiently counting a number of minuteparticles such as bacteria and microorganisms contained in a samplesolution by using dielectrophoresis. In the method in Patent Literature1, a detection region on a detection substrate, on which a pair of thinfilm electrodes are formed, is segmented into detection segments thatdivide the entire length of each linear portion of the electrode gapinto several tens of pieces. On each of the detection segments, thenumber of minute particles each of which having one end trapped to anedge of the electrodes by dielectrophoresis is counted in the method inPatent Literature 1. Then, sequentially scanning the detection segmentsto sum the number of minute particles is done, whereby the total numberof minute particles that exist in the detection region is detected.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Unexamined Patent Application    Publication No. 2008-196860

SUMMARY OF INVENTION Technical Problem

In the microorganism detection method in Patent Literature 1,dielectrophoresis is applied to trap one end of a minute particle to anedge of the electrodes on each detection segment, and then theimmobilized minute particles are counted one by one. Therefore, it takestime and effort to detect the total number of minute particles, and theeffort is wasted.

An object of the present invention is to provide an inspection device,an inspection system, and an inspection method capable of easilyinspecting the amount of bacteria, cells, and the like contained in asample liquid.

Solution to Problem

The inspection device according to one aspect of the present inventionis a device for inspecting an amount of dielectric particles containedin a sample liquid. The inspection device includes a dielectriccollection unit, a pump unit and an AC voltage supply unit. Thedielectric collection unit includes at least one pair of electrodes anda flow channel extending in a predetermined direction on the pair ofelectrodes. The pump unit is configured to feed the sample liquid tofollow the flow channel in the predetermined direction. The AC voltagesupply unit is configured to supply, to the pair of electrodes, an ACvoltage with a predetermined frequency to cause dielectrophoresis fordielectric particles in the fed sample liquid. The dielectric collectionunit includes a plurality of slit regions aligned in the predetermineddirection between the pair of electrodes. Each of the plurality of slitregions is separated from each other within the flow channel.

The inspection system according to one aspect of the present inventionincludes the inspection device and a display unit. The inspection devicefurther includes an imaging unit for capturing the image of apredetermined region in which the plurality of slit regions are aligned.The display unit displays the image captured by the imaging unit of theinspection device.

The inspection method according to one aspect of the present inventionis a method for inspecting an amount of dielectric particles containedin a sample liquid. The method includes feeding the sample liquid tofollow a flow channel in a predetermined direction in a dielectriccollection unit, the dielectric collection unit including at least onepair of electrodes and the flow channel extending in the predetermineddirection on the pair of electrodes. The method includes supplying, tothe pair of electrodes, an AC voltage with a predetermined frequency tocause dielectrophoresis for dielectric particles in the fed sampleliquid. The method includes counting slits saturated with the dielectricparticles among a plurality of slits aligned in the predetermineddirection between the pair of electrodes in the dielectric collectionunit.

According to the inspection device, the inspection system, and theinspection method according to the present invention, counting the slitssaturated with dielectric particles such as bacteria and cells allowsthe amount of bacteria, cells, and the like contained in the sampleliquid to be easily inspected.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of the inspectionsystem according to a first embodiment.

FIGS. 2A to 2E are diagrams for explaining the collection unit in thedielectrophoresis device of the present system.

FIG. 3 is an enlarged view of the wiring region of the film electrodesin the collection unit.

FIG. 4 is an enlarged view of the microelectrode unit in the wiringregion.

FIGS. 5A and 5B are diagrams for explaining the principle of the presentinspection method.

FIGS. 6A to 6E are diagrams for explaining an imaging method in thepresent system.

FIG. 7 is a graph showing a first experimental result of the inspectionmethod according to the first embodiment.

FIGS. 8A to 8E are captured images in the first experiment of thepresent inspection method.

FIGS. 9A to 9F are captured images in the second experiment of thepresent inspection method.

FIGS. 10A to 10C are images showing the states of the microelectrodeunit in the multistage switching method according to a secondembodiment.

FIG. 11 is a flowchart showing multistage switching processing in thepresent system.

FIGS. 12A to 12D are diagrams for explaining the imaging processing instep S4 in FIG. 11.

FIG. 13 is a graph showing an experimental result of the multistageswitching method.

FIG. 14 is a flowchart showing a modified example of the multistageswitching processing.

EMBODIMENT OF THE INVENTION

In the following, embodiments of an inspection device, an inspectionsystem, and an inspection method using dielectrophoresis according tothe present invention will be described with reference to theaccompanying drawings. It should be noted that in each of the followingembodiments, the same reference numerals are given to the sameconstituent elements.

First Embodiment 1. Configuration 1-1. System Configuration

The overall configuration of the inspection system according to a firstembodiment will be described with reference to FIG. 1. FIG. 1 is a blockdiagram showing a configuration of the inspection system according tothe first embodiment. The inspection system according to the presentembodiment includes a dielectrophoresis device 1, a control device 20,an information processing device 21, and a waste liquid chamber 22. Thepresent inspection system is a system for performing inspection ofbacteria and the like by using dielectrophoresis of bacteria and cellsin a sample liquid (sample) in the dielectrophoresis device 1. In thepresent system, the dielectrophoresis device 1 is controlled by thecontrol device 20, and the state in which inspection objects such asbacteria are collected in the dielectrophoresis device 1 is displayed inthe information processing device 21.

The dielectrophoresis device 1 includes a pump unit 10, an AC(alternating-current) voltage supply unit 11, an imaging unit 12, and acollection unit 3. The dielectrophoresis device 1 is an example of aninspection device in the present embodiment.

The pump unit 10 is constituted by, for example, a syringe pump, andincludes a driver 10 a and a sample syringe 10 b. The driver 10 a isconfigured to include a motor or the like, and drive control isperformed by the control device 20. The sample syringe 10 b is a syringefor holding a sample liquid. The collection unit 3 is connected to theliquid feeding part of the sample syringe 10 b. In the pump unit 10, thevelocity of flow and the amount of flow are appropriately set by thedrive control of the driver 10 a, whereby the sample liquid is fed fromthe sample syringe 10 b to the collection unit 3.

The collection unit 3 includes a flow channel 13 through which thesample liquid flows in a predetermined direction (liquid flow direction)and a microelectrode unit 30 provided in the flow channel 13. The sampleliquid fed from the pump unit 10 flows through the flow channel 13 inthe collection unit 3 to be drained into the waste liquid chamber 22.The microelectrode unit 30 includes an electrode group formed on theorder of micron. In the collection unit 3, when the sample liquid flowson the microelectrode unit 30 in the flow channel 13, a predetermined ACvoltage is supplied from the AC voltage supply unit 11 to themicroelectrode unit 30. Thus, the bacteria and the like of theinspection objects in the sample liquid cause dielectrophoresis to becollected by the microelectrode unit 30. The collection unit 3 is anexample of a dielectric collection unit for collecting dielectricparticles such as bacteria in the microelectrode unit 30. Details of theconfiguration of the collection unit 3 will be described below.

The AC voltage supply unit 11 includes, for example, a functiongenerator. The AC voltage supply unit 11 generates an AC voltage havinga desired frequency and voltage amplitude under the control of thecontrol device 20 to supply the AC voltage to the microelectrode unit 30of the collection unit 3.

The imaging unit 12 includes an image pickup element 12 a such as a CCDimage sensor or a CMOS image sensor, and an optical microscope module 12b. The optical microscope module 12 b may be a phase contrast microscopeor an epi illumination microscope. The optical microscope module 12 bmay be configured to be switchable between a phase contrast microscopeand an epi illumination microscope with lens exchange or the like. Inaddition, when fluorescence observation is performed, a fluorescencefilter can be appropriately used. The imaging unit 12 captures an imageof a predetermined region in the microelectrode unit 30 in thecollection unit 3 (details will be described below) and outputs thecaptured image to the information processing device 21. The imagingoperation of the imaging unit 12 may be controlled by the control device20 or may be controlled by the information processing device 21.

The control device 20 includes, for example, a CPU and an MPU. Thecontrol device 20 controls the operation of the dielectrophoresis device1 such as liquid feeding of the sample liquid by the pump unit 10 andsupply of the AC voltage by the AC voltage supply unit 11. The controldevice 20 includes an internal memory such as a flash memory, andimplements various kinds of functions by performing arithmeticprocessing using various data or the like based on a program stored inthe internal memory. The control device 20 may include a hardwarecircuit such as an electronic circuit designed for exclusive use or areconfigurable electronic circuit (ASIC, FPGA, or the like). Thefunction of the control device 20 may be implemented by cooperation ofhardware and software, or may be implemented only by hardware(electronic circuit).

The information processing device 21 includes, for example, a personalcomputer. The information processing device 21 includes a liquid crystaldisplay or an organic electroluminescent display (display unit), anddisplays a captured image of the imaging unit 12. The informationprocessing device 21 includes an internal memory such as a flash memoryand implements various kinds of functions based on a program stored inthe internal memory. For example, the information processing device 21performs image analysis of the captured image of the imaging unit 12 andcounts the number of regions (slits) meeting predetermined conditions inthe captured image. The information processing device 21 may control theimaging operation of the imaging unit 12. In addition, the informationprocessing device 21 and the control device 20 may be integrallyconfigured by implementing various kinds of functions of the controldevice 20 in the information processing device 21. The informationprocessing device 21 is an example of a display unit in the presentembodiment and is an example of an image analysis unit for analyzing theimaging result of the imaging unit 12.

The waste liquid chamber 22 is a chamber for storing the sample liquidflowing through the collection unit 3 of the dielectrophoresis device 1.The waste liquid chamber 22 may be incorporated inside thedielectrophoresis device 1.

1-2. Configuration of Collection Unit

The configuration of the collection unit 3 will be described below withreference to FIGS. 2A to 4.

FIG. 2A shows a plan view of the collection unit 3. FIG. 2B is across-sectional view taken along the line A-A′ of the collection unit 3shown in FIG. 2A. The collection unit 3 has an approximately rectangularflat plate shape as shown in FIG. 2A. In addition, as shown in FIG. 2B,the collection unit 3 includes a cover plate 31, a spacer 32, and anelectrode film 33, and has a structure in which these are sequentiallysuperimposed in the thickness direction.

FIG. 2C shows a plan view of the cover plate 31 in the collection unit3. FIG. 2D shows a plan view of the spacer tape 32. FIG. 2E shows a planview of the electrode film 33.

The cover plate 31 is a plate member formed of, for example, atransparent acrylic plate or the like. As shown in FIG. 2C, the coverplate 31 is provided with two insertion holes 31 a and 31 b and acut-away part 31 c. The insertion holes 31 a and 31 b respectivelycorrespond to the start point and the end point of the flow channel 13in the collection unit 3 (see FIG. 2A). The cut-away part 31 c is famedin a position corresponding to an electrode pad 33 a on the electrodefilm 33 in the cover plate 31.

The spacer 32 is a member formed of, for example, a transparent PET(polyester) tape. In the spacer 32, a rectangular hole 32 acorresponding to the flow channel 13 and a cut-away part 32 b having thesame shape as the cut-away part 31 c of the cover plate 31 are formed.The spacer 32 adheres to the cover plate 31 and the electrode film 33 onthe respective principal surfaces with an adhesive such as 3M(registered trademark) 9969, and the space between the cover plate 31and the electrode film 33 (that is, the height of the flow channel 13)is fixed to a predetermined width (for example, 0.1 mm).

The electrode film 33 is a member provided with the microelectrode unit30 on a transparent film base material such as a PEN (polyethylenenaphthalate) film. The microelectrode unit 30 is electrically connectedto the electrode pad 33 a in the wiring region (details will bedescribed below) on the principal surface of the electrode film 33. Themicroelectrode unit 30 and the electrode pad 33 a are formed of ametallic material such as chromium, for example, by vapor deposition orsputtering.

The collection unit 3 is electrically connected to the AC voltage supplyunit 11 at the electrode pad 33 a (see FIG. 1). As shown in FIG. 2A, theelectrode pad 33 a is exposed by the cut-away parts 31 c and 32 b in astate where the cover plate 31, the spacer 32, and the electrode film 33are superimposed on each other. Therefore, the collection unit 3 caneasily be electrically connected to the AC voltage supply unit 11.

The flow channel 13 of the collection unit 3 is formed by the spacer 32,which closely sticks the cover plate 31 to the electrode film 33 with apredetermined space apart around the rectangular hole 32 a. By removablyconnecting the sample syringe 10 b and the waste liquid chamber 22respectively to the two insertion holes 31 a and 31 b positioned at bothends of the flow channel 13, causing the sample liquid to flow throughthe flow channel 13 can be easily achieved. As described above,electrical connection and flow channel connection in the collection unit3 can be easily performed. Thus, the collection unit 3 can be easilythrown away or reused after collecting bacteria and the like in thedielectrophoresis device 1.

FIG. 3 is an enlarged view of the wiring region in the electrode film 33in FIG. 2E. In the present embodiment, the microelectrode unit 30 in theelectrode film 33 includes two sets of electrode pairs CH1 and CH2. TheAC voltage from the AC voltage supply unit 11 is supplied to each of theelectrodes of the first and second electrode pairs CH1 and CH2 throughthe electrode pad 33 a. The first and second electrode pairs CH1 and CH2are formed line-symmetrically with respect to the center line L1. In thefollowing, the explanation of the first electrode pair CH1 will beexemplified.

The first electrode pair CH1 includes two electrodes 41 and 42. Each ofthe electrodes 41 and 42 has a pectinate shape arranged at equalintervals. A plurality of protruding parts in the pectinate shape of thetwo electrodes 41 and 42 are alternately arranged at predeterminedintervals in the liquid flow direction of the flow channel 13. Eachprotruding part of the electrodes 41 and 42 extends in a directionintersecting (orthogonal to) the liquid flow direction. The samearrangement also applies to electrodes 41 and 42 of the second electrodepair CH2.

FIG. 4 is an enlarged view of the microelectrode unit 30 in a region Rinear the edge of the flow channel 13. In the microelectrode unit 30,slit shaped regions Rs each having a predetermined width W2 (hereinafterreferred to as “slit region”) are formed by a slit between eachprotruding part of the electrodes 41 and 42 on the flow channel 13. Asshown in FIG. 4, a plurality of slit regions Rs align in the liquid flowdirection between the pair of electrodes 41 and 42. The width W2 of eachslit region Rs is set to a predetermined value, for example, from 10 μmto 20 μm. On the other hand, the width W1 of a protruding part of theelectrodes 41 and 42 is, for example, 100 μm. The width W2 of the slitregion Rs may be set within the range of 1 μm to 50 μm.

In the present embodiment, the microelectrode unit 30 and the flowchannel 13 are set in such a manner that each protruding part of theelectrodes 41 and 42 is forced out the flow channel 13 by apredetermined length Δd. In other words, the region connecting theplurality of slit regions Rs between the pair of electrodes 41 and 42 onthe electrode film 33 is arranged outside the flow channel 13. Thus, theplurality of slit regions Rs, which are aligned in the predetermineddirection in which the flow channel 13 extends (liquid flow direction),are separated from each other without being connected in the flowchannel 13. For example, the length Δd by which both ends of theelectrodes 41 and 42 is out of the flow channel 13 is set to 0.3 mm ascompared with the width W3 of the flow channel 13 (see FIG. 3) being setto 3 mm. In addition, the protruding part thickness of each of theelectrodes 41 and 42 is, for example, about 100 nm.

In the present inspection system, when the dielectrophoresis of bacteriaand the like is performed in the dielectrophoresis device 1, as shown inFIG. 3, a region Rc in which the protruding parts of the electrodes 41and 42 are sequentially aligned from the upstream side of the flowchannel 13 in the microelectrode unit 30 is captured by the imaging unit12. Thus, a captured image in which it is easy to measure the number ofdisplayed slit regions Rs, that is, to count the slits (Rs) can beobtained.

If the slit regions Rs are connected to each other in the flow channel13, it is considered to cause, for example, a situation such thatbacteria and the like collected in the slit regions Rs on the upstreamside move to the slit regions Rs on the downstream side while thedielectrophoresis force between the electrodes 41 and 42 is maintained.On the contrary, separating each slit region Rs in the flow channel 13as described above allows the collected bacteria and the like betweenthe plurality of slit regions Rs to be prevented from moving, andinspection of the amount of bacteria by counting the slits (Rs) to beeasily performed (hereinafter, “slit region Rs” may be abbreviated as“slit Rs”).

2. Operation and Inspection Method

The operation of the present system and the inspection method in thepresent system will be described below.

2-1. Principle of Inspection Method

FIGS. 5A and 5B are explanatory diagrams of the principle of theinspection method according to the present embodiment.

In the inspection system and the inspection method according to thepresent embodiment, bacteria and the like of the inspection objectscontained in the sample liquid are collected by using dielectrophoresis.As shown in FIG. 5A, when an AC voltage with a frequency ω is suppliedbetween the electrodes 41 and 42, the dielectrophoresis force F_(DEP)acting on bacteria such as viable bacteria and dead bacteria in thesample liquid flowing through the flow channel 13 is expressed by thefollowing equation.

F _(DEP)=2πr ³ε_(m)Re[K(ω)]∇E ²  (1)

In the above equation (1), r is the radius of dielectric particles suchas viable bacteria and dead bacteria of the inspection objects, ε_(m) isthe dielectric constant of the medium of the sample liquid, and E is theintensity of the electric field. Re[X] represents the real part of thecomplex number X. K(ω) is the Clausius-Mossotti factor and is expressedby the following equation.

K(ω)=(ε_(p)*−ε_(m)*)/(ε_(p)*+2ε_(m)*)  (2)

In the above equation (2), ε_(p)* (=ε_(p)+ρ_(p)/(jω)) is the complexdielectric constant of the dielectric particles (ε_(p) is the dielectricconstant of the dielectric particles and ρ_(p) is the conductivitythereof). In addition, ε_(m)* (=ε_(m)+ρ_(m)/(jω)) is the complexdielectric constant of the medium (ρ_(m) is the conductivity of themedium).

When Re[K(ω)]>0 in the above equation (1), a positive dielectrophoresisforce F_(DEP) with respect to the installation direction of theelectrodes 41 and 42 acts on the dielectric particles, and thedielectric particles are attracted to the vicinities of the electrodes41 and 42 to be absorbed to the slit Rs. On the other hand, whenRe[K(ω)]<0, a negative dielectrophoresis force F_(DEP) acts on thedielectric particles, and the dielectric particles repel the electrodes41 and 42. Therefore, appropriately setting the frequency ω allowsinspection objects to be selectively adsorbed to the slit Rs whileremoving impurities and the like other than the inspection objects.

Bacteria in the sample liquid are collected in the slit Rs by the actionof positive dielectrophoresis force F_(DEP). Since a bacterium has apredetermined size, the slit Rs is filled with bacteria to be saturatedwhen a certain amount of bacteria are collected in the slit Rs. In thepresent system, saturation is reached in order from the upstream slit Rsin the flow channel 13, since the microelectrode unit 30 is set in sucha manner that a plurality of slits Rs are arranged at predeterminedintervals in the liquid flow direction in the flow channel 13.

Thus, in the present inspection method, the amount of bacteria and thelike contained in the sample liquid is measured as follows by the userof the present system.

First, the amount of bacteria and the like per slit Rs to be collectedwhen saturation occurs (saturation amount) is obtained in advance.

Next, the dielectrophoresis device 1 is controlled with the controldevice 20, whereby an AC voltage with a predetermined frequency issupplied from the AC voltage supply unit 11 to the microelectrode unit30 in the flow channel 13 while a sample liquid flows from the pump unit10 to the flow channel 13 of the collection unit 3, and a positivedielectrophoresis force is acted on the inspection objects.

Next, the region Rc in which the slits Rs in the microelectrode unit 30are aligned (see FIG. 3) is captured, and the number of saturated slitsRs are counted in the captured image. The number of slits may be countedby image analysis performed on the captured image by the informationprocessing device 21 or by the user based on the captured imagedisplayed on the information processing device 21. Instead of imagingthe region Rc, the user may directly look through the optical microscopeto count the saturated slits Rs.

The amount of bacteria and the like of the inspection objects containedin the sample liquid is obtained by the product of the previouslyobtained saturation amount and the number of slits of the countingresult. Therefore, by measuring the number of slits saturated withbacteria and the like trapped, the inspection objects contained in thesample liquid can be easily quantitatively evaluated.

The saturation amount of slit Rs can be calculated based on the type andsize of bacteria and the like of the inspection objects. Depending onthe inspection objects, the frequency w of the AC voltage is set in sucha manner that a positive dielectrophoresis force acts, and the voltageamplitude of the AC voltage and the velocity of flow in the flow channel13 are also controlled appropriately. Thus, various inspection objectscan be selectively collected and quantitatively evaluated easily(details will be described below).

For example, frequency control can switch whether or not to distinguishbetween viable bacteria (active bacteria) and dead bacteria (damagedbacteria) in bacteria. FIG. 5A shows an example of collecting viablebacteria and dead bacteria together. For example, an AC voltage to theelectrodes 41 and 42 at the frequency ω=100 kHz is supplied to cause apositive dielectrophoresis force to act on both viable bacteria and deadbacteria. According to this, both viable bacteria and dead bacteria canbe collected distinguished from others and can be quantitativelyevaluated.

FIG. 5B shows an example of selectively collecting viable bacteria. Inthe example shown in FIG. 5B, after the operation at the frequency ω=100kHz as shown in FIG. 5A, the frequency ω is raised to 3 MHz. Then, whilea positive dielectrophoresis force acts on viable bacteria, the positivedielectrophoresis force does not act on dead bacteria. Thus, only theviable bacteria can be adsorbed to the slit Rs, and the amount of viablebacteria other than dead bacteria can be easily quantitativelyevaluated.

2-2. Evaluation Method

In the present system, various observation methods are available tocount the slits saturated with bacteria and the like in themicroelectrode unit 30, and to quantitatively evaluate bacteria and thelike. In the following, evaluation method a of the amount of bacteria inthe present system will be described with reference to FIGS. 6A to 6E.

FIGS. 6A and 6B show imaging examples of states before and after theperformance of dielectrophoresis in the phase contrast observationmethod. FIGS. 6C and 6D show imaging examples of states before and afterthe performance of dielectrophoresis in the bright field observationmethod. FIG. 6E shows an imaging example of a state after theperformance of dielectrophoresis in the fluorescence observation method.

In the present embodiment, when phase contrast observation is performed,the phase contrast microscope is used in the imaging unit 12 (see FIG.1). Then, in the initial state before the performance ofdielectrophoresis, the region Rc of the microelectrode unit 30 isobserved (imaged) as shown in FIG. 6A. That is, the electrodes 41 and 42appear dark while the slit Rs appears bright. This is because theelectrodes 41 and 42 are opaque while the slit Rs is transparent.

On the other hand, when dielectrophoresis is performed so that bacteriaare collected in the slit Rs, the saturated slit Rs becomes dark asshown in FIG. 6B. This is because the slit Rs becomes opaque due to theaccumulation of bacteria in the saturated slit Rs. Therefore, bycounting the number of slits that remain bright as before and after thedielectrophoresis or counting the number of darkened slits, the amountof bacteria can be quantitatively evaluated.

When bright field observation is performed, an epi illuminationmicroscope is used in the imaging unit 12. Then, in the initial statebefore the performance of dielectrophoresis, the region Rc of themicroelectrode unit 30 is observed as shown in FIG. 6C. That is, boththe electrodes 41 and 42 and the slit Rs appear dark with the adjustmentof the reflected light of the light emitted from the epi illuminationmicroscope.

On the other hand, when dielectrophoresis is performed so that bacteriaare collected in the slit Rs, the saturated slit Rs appears bright withthe reflected light from the collected bacteria as shown in FIG. 6D. Inthis case, by counting the number of slits appearing bright after thedielectrophoresis, the amount of bacteria can be quantitativelyevaluated.

When fluorescence observation is performed, fluorescent labels are usedfor inspection objects in the sample liquid. Further, in the imagingunit 12, the epi illumination microscope in which, for example, afluorescence filter or the like is appropriately set (fluorescencemicroscope) is used. The initial state before the dielectrophoresis inthis case is the same as in the case of bright field observation (FIG.6C). On the other hand, when dielectrophoresis is performed in thedielectrophoresis device 1 so that bacteria are collected in the slitRs, the saturated slit Rs emits fluorescence as shown in FIG. 6E.Therefore, the slit Rs saturated after the dielectrophoresis appearsmore clearly, and it is easier to count the number of slits.

2-3. Experimental Results

In the following, experimental results of the inspection methodaccording to the present embodiment will be described with reference toFIGS. 7 to 9F. FIG. 7 is a graph showing a first experimental result ofthe present inspection method. FIGS. 8A to 8E are captured images in thefirst experiment of the present inspection method.

In the first experiment shown in FIGS. 7 and 8A to 8E, coli bacteria(ATCC 11775) are used as experimental bacteria of the inspectionobjects. The above inspection method is performed a plurality of timesby changing the amount of experimental bacteria in the sample liquid. Asthe imaging method, a phase contrast observation method is adopted (seeFIGS. 6A and 6B).

In FIG. 7, the horizontal axis represents the number of slits in whichthe experimental bacteria are collected and filled until theexperimental bacteria are saturated. The vertical axis represents theamount of experimental bacteria, and the unit of the vertical axis is10⁶ CFU (colony forming unit).

FIGS. 8A to 8E show captured images corresponding to the respectiveexperimental results plotted in the graph in FIG. 7. FIG. 8A shows acaptured image in the initial state (0 CFU). FIGS. 8B to 8E show thecaptured images when the experimental bacteria amount is set to 0.7×10⁶CFU, 1.4×10⁶ CFU, 2.8×10⁶ CFU, and 4.2×10⁶ CFU, respectively.

In FIG. 8A, all the eight slits appear bright corresponding to the factthat experimental bacteria are not collected in the initial state. InFIG. 8B, one slit, which appears bright at the left end in FIG. 8A, isdark. In FIG. 8C, one more slit is dark from the state in FIG. 8B. Thedarkened slit is a slit saturated (filled) with experimental bacteriacontained in the sample liquid. In FIG. 8C, since the experimentalbacteria amount approximately twice as large as that in FIG. 8B (1.4×10⁶CFU) is set, it is understood that the number of darkened slits actuallycorresponds to the experimental bacteria amount contained in the sampleliquid.

Also in FIGS. 8D and 8E, the number of darkened slits increasesaccording to the increase of the experimental bacteria amount to 2.8×10⁶CFU and 4.2×10⁶ CFU in order. As shown in FIG. 7, the number of darkenedslits in FIGS. 8A to 8E is proportional to the experimental bacteriaamount in each case. As described above, it is confirmed that countingthe number of darkened slits allows the bacteria contained in the sampleliquid to be easily and quantitatively evaluated.

FIGS. 9A to 9F are captured images in the second experiment of thepresent inspection method. In the second experiment, S. Cerevisiae isused as the experimental bacterium and epi illumination observationmethod is adopted as the imaging method (see FIGS. 6C and 6D).

In FIGS. 9A to 9F, the saturated slit appears brighter based on the epiillumination observation method. In FIGS. 9A to 9F, the experimentalbacteria amount is increased sequentially. In FIG. 9A, 0.5 slit appearsbright. Subsequently, 1.0 slit in FIG. 9B, 2.0 slits in FIG. 9C, 3.5slits in FIG. 9D, 4.0 slits in FIG. 9E, and 5.5 slits in FIG. 9F appearbright. From the view of FIGS. 9A to 9F, based on the epi illuminationobservation method in the second experiment, it is confirmed thatcounting the number of brightened slits allows the bacteria contained inthe sample liquid to be easily and quantitatively evaluated.

3. Summary

As described above, the dielectrophoresis device 1 according to thepresent embodiment is an inspection device for inspecting an amount ofthe dielectric particles contained in the sample liquid. Thedielectrophoresis device 1 includes the dielectric collection unit 3,the pump unit 10, and the AC voltage supply unit 11. The dielectriccollection unit 3 includes at least the pair of electrodes 41 and 42 andthe flow channel 13 extending in the predetermined liquid flow directionon the pair of electrodes 41 and 42. The pump unit 10 feeds the sampleliquid to follow the flow channel 13 in the liquid flow direction. TheAC voltage supply unit 11 supplies, to the pair of electrodes 41 and 42,the AC voltage with the predetermined frequency to causedielectrophoresis for dielectric particles in the sample liquid. Thedielectric collection unit 3 includes the plurality of slit regions Rsaligned in the liquid flow direction between the pair of electrodes 41and 42. Each of the plurality of slit regions Rs is separated from eachother within the flow channel 13.

Accordingly, in the plurality of slit regions Rs separated from eachother aligned in the liquid flow direction in the flow channel 13, slitsare saturated in order from the upstream side and can be counted in theorder. Thus, the amount of bacteria, cells, and the like contained inthe sample liquid can be easily inspected.

The inspection method according to the present embodiment is aninspection method for inspecting the amount of dielectric particlescontained in the sample liquid. The present method includes: feeding thesample liquid in such a manner as to advance in a predetermineddirection in the collection unit 3 including at least the pair ofelectrodes CH1 and CH2 arranged alternately at equal intervals of theplurality of slits Rs in the predetermined direction; supplying the ACvoltage with the predetermined frequency to the pair of electrodes tocause dielectrophoresis for the dielectric particles in the fed sampleliquid; and counting the slits saturated with the dielectric particlesin the collection unit 3.

The inspection system according to the present embodiment includes thecollection unit 3, the pump unit 10, the AC voltage supply unit 11, theimaging unit 12, and the information processing device 21. Thecollection unit 3 includes at least the pair of electrodes CH1 and CH2arranged alternately at equal intervals of the plurality of slits Rs inthe predetermined direction. The pump unit 10 feeds the sample liquid insuch a manner that the sample liquid advances in the predetermineddirection in the collection unit 3. The AC voltage supply unit 11supplies the AC voltage with the predetermined frequency to the pair ofelectrodes CH1 and CH2 to cause dielectrophoresis for the dielectricparticles in the fed sample liquid. The imaging unit 12 captures animage of a predetermined region Rc in which the plurality of slits Rsare aligned in the collection unit 3. The information processing device21 analyzes the imaging result to count the slits Rs saturated with thedielectric particles.

Accordingly, counting the slits saturated with dielectric particles suchas bacteria and cells allows the amount of bacteria, cells, and the likecontained in the sample liquid to be easily inspected.

Second Embodiment

In the present inspection system, the supply voltage control over theelectrode pairs CH1 and CH2 in the microelectrode unit 30 may beswitched in stages. Multistage switching methods are available toperform quantitative evaluation with high accuracy filling each slit Rswith bacteria and the like as follows. A method of once holding thebacteria and the like of the inspection objects in the electrode pairCH1 on the upstream side and imaging the held bacteria and the like inthe electrode pair CH2 on the downstream side will be described.

FIGS. 10A to 10C are images showing the states of the electrode pairsCH1 and CH2 of the microelectrode unit in the multistage switchingmethod according to the second embodiment. FIG. 11 is a flowchartshowing multistage switching processing according to the presentembodiment.

First, the control device 20 controls the AC voltage supply unit 11 tosupply an AC voltage with a first frequency to the first electrode pairCH1 for a predetermined period (for example, 1 to 10 minutes) (S1). Thefirst frequency is a frequency for causing a positive dielectrophoresisforce to act on the bacteria and the like of the objects of collection,and is set to, for example, 100 kHz (to collect viable bacteria and deadbacteria). The predetermined period can be set appropriately accordingto the inspection objects.

FIG. 10A shows an image of the first and second electrode pairs CH1 andCH2 after the processing in step S1 is performed. The image shown inFIG. 10A is an image based on the fluorescence observation (see FIG. 6E)(the same applies to FIGS. 10B and 10C). Performing the processing instep S1 for a predetermined period causes bacteria to be collected in aplurality of slits and held in the first electrode pair CH1 in FIG. 10A.

Next, the control device 20 stops supplying the AC voltage with thefirst frequency from the AC voltage supply unit 11 to the firstelectrode pair CH1 (S2). Then, no dielectrophoresis force acts on thebacteria in the first electrode pair CH1, and thus the held bacteria isreleased from the first electrode pair CH1 (see FIG. 10B).

Next, the control device 20 supplies the AC voltage with the firstfrequency from the AC voltage supply unit 11 to the second electrodepair CH2 (S3). In step S3, the control device 20 also controls the pumpunit 10 to flow the sample liquid in the liquid flow direction with theamount of flow and the velocity of flow set appropriately.

FIG. 10B shows an image of the first and second electrode pairs CH1 andCH2 at the start of the processing in step S3. In FIG. 10B, the bacteriaheld in the first electrode pair CH1 moves in the liquid flow direction,and some of the bacteria reach the second electrode pair CH2.

FIG. 10C shows an image of the first and second electrode pairs CH1 andCH2 after a lapse of a predetermined period from the state shown in FIG.10B. The processing in step S3 is performed for a predetermined periodfrom the state shown in FIG. 10B, whereby bacteria are intensivelycollected in the upstream slit in the second electrode pair CH2 in FIG.10C. It is considered that once holding the bacteria in the firstelectrode pair CH1 in step S1 causes the bacteria to move along thevicinity of the bottom of the flow channel in steps S2 and S3 and thedielectrophoresis force to act efficiently when the bacteria reach thesecond electrode pair CH2 positioned at the bottom of the flow channel.

Next, the control device 20 captures an image from the imaging unit 12 aspecific region in which slits are aligned in the second electrode pairCH2 (S4). The region to be imaged is, for example, a region includingthe most upstream slit in the second electrode pair CH2 (see FIG. 12).The control of the imaging unit 12 in step S4 may be performed from theinformation processing device 21.

According to the above processing, the bacteria are once held in thefirst electrode pair CH1 on the upstream side in step S1, and the heldbacteria are moved to the downstream side, and then collected again inthe second electrode pair CH2. Therefore, the probability that bacteriaare collected in order from the upstream slit can be improved in thesecond electrode pair CH2, and the accuracy of quantitative evaluationby counting the number of slits filled with bacteria can be improved.

FIGS. 12A to 12D are diagrams for explaining the imaging processing instep S4 in FIG. 11. In FIGS. 12A to 12D, the slits in the secondelectrode pair CH2 are filled with bacteria in order from the upstreamside. Therefore, imaging the region enclosed by the broken line in thefigure allows quantitative evaluation to be easily performed by countingthe number of slits.

FIG. 13 is a graph showing an experimental result of the multistageswitching method. In FIG. 13, the horizontal axis represents the numberof slits filled with experimental bacteria in the second electrode pairCH2. The vertical axis represents the amount of experimental bacteria,and the unit of the vertical axis is CFU.

In the experiment shown in FIG. 13, coli bacteria (ATCC 11775) are usedas experimental bacteria. The inspection method by multistage switchingmethod is performed a plurality of times by changing the amount ofexperimental bacteria in the sample liquid. The first frequency of theAC voltage is set to 100 kHz and the voltage amplitude is set to 5volts. The amount of experimental bacteria on the vertical axis iscalculated from the viable bacteria evaluation method by the WST-1method using a microplate reader. According to FIG. 13, it is confirmedthat bacteria contained in the sample liquid can be easily evaluatedquantitatively by counting the number of slits sequentially filled inorder from the upstream in the downstream electrode pair CH2 in themultistage switching method.

In the above processing, the AC voltage with one kind of frequency(first frequency) is supplied in the electrode pairs CH1 and CH2, butthe frequency of the AC voltage supplied to the electrode pairs CH1 andCH2 may be switched. In the following, an example of a method forseparating viable bacteria from dead bacteria by switching the frequencyof the AC voltage will be described with reference to FIG. 14.

FIG. 14 is a flowchart showing a modified example of the multistageswitching processing in FIG. 13. In the processing shown in FIG. 14,instead of stopping the supply of the AC voltage to the first electrodepair CH1 in step S2 in FIG. 13, the frequency of the AC voltage isswitched from the first frequency to the second frequency (S2A). Thesecond frequency is a frequency for causing a positive dielectrophoresisforce to act on the bacteria and the like as the objects to be held inthe first electrode pair CH1, and is set to, for example, 3 MHz (onlyviable bacteria are held). Then, out of the bacteria held in step S1 inthe first electrode pair CH1, the dielectrophoresis force does not actonly on dead bacteria, and the dead bacteria are released from the firstelectrode pair CH1.

Next, in step S3, the AC voltage with the first frequency capable ofcollecting dead bacteria is supplied to the second electrode pair CH2.Therefore, only the dead bacteria are collected in the second electrodepair CH2 in order from the upstream slit, and the viable bacteria remainheld in the first electrode pair CH1. Therefore, in the following stepS4, capturing of the specific region of the second electrode pair CH2allows a captured image in a state filled with dead bacteria in orderfrom the upstream slit to be obtained.

With the above processing, among the viable bacteria and dead bacteriaheld in the first electrode pair CH1, only dead bacteria are selectivelyre-collected in the second electrode pair CH2. Accordingly, quantitativeevaluation can be easily performed with the distinction between viablebacteria and dead bacteria.

In addition, in the above processing, when viable bacteria are used asinspection objects, in step S4, the region of measurement in the firstelectrode pair CH1 may be imaged. In addition, when both viable bacteriaand dead bacteria are compared, in step S4, a region including the firstand second electrode pairs CH1 and CH2 may be imaged.

Other Embodiments

In the above embodiments, bacteria and cells are exemplified asinspection objects of the present system. The inspection objects of thepresent system are not limited to bacteria and cells, and may be variousdielectric particles, and may be, for example, microorganisms, fungi,spores, and viruses.

In the above embodiments, the collection unit 3 in which two electrodepairs CH1 and CH2 are provided for one flow channel 13 is described. Theflow channel and the electrode pair in the collection unit are notlimited to this, and, for example, a plurality of flow channels orbranched flow channels may be provided, or one or more electrode pairsmay be provided for each flow channel.

Although the processing of each step in the flowcharts in FIGS. 11 and14 is performed by the control device 20 in the above embodiments, theprocessing may be performed by the user of the present system or may beperformed by the user's operation of the control device 20.

In the above embodiments, the first frequency of the AC voltage suppliedin step S1 in FIG. 11 exemplifies 1 kHz. When only the viable bacteriaare to be inspection objects, for example, the first frequency of the ACvoltage supplied in step S1 may be set to a value at which thedielectrophoresis force acts only on viable bacteria, such as 3 MHz.Thus, in step S4 in FIG. 11, a captured image of the slits filled inorder only with viable bacteria in the second electrode pair CH2 isobtained.

In the above embodiments, the illustrated example is that eachprotruding part and each slit of the electrodes 41 and 42 of thecollection unit 3 (dielectric collection unit) extend in a directionorthogonal to the liquid flow direction. The slits in the dielectriccollection unit need not be orthogonal to the liquid flow direction (thelongitudinal direction of the flow channel 13), and may cross at apredetermined angle (for example, 45 degrees or more) with respect tothe liquid flow direction.

In the above embodiments, the illustrated example is that the slitbetween each protruding part of the electrodes 41 and 42 is linearlyformed with the predetermined width W2. The shape of the slit may be,for example, curved or bent, or the width W2 for each slit may bedifferent. Further, the plurality of slits may not be parallel to eachother, and for example, the slits may be arranged side by side within arange of a predetermined angle.

In the above embodiments, the dielectrophoresis device 1 (inspectiondevice) including an imaging unit 12 is described. The inspection deviceaccording to the present invention may not include the imaging unit 12.For example, he instead of (or in addition to) the imaging unit 12, theinspection device may include a microscope having an eyepiece or thelike for the user to directly observe the region Rc.

In addition, the image analysis by the inspection system in the aboveembodiments may be performed by, for example, an area analysis method.Specifically, the image analysis unit (information processing device 21)calculates the area of the saturated slits Rs in the region Rc of theobservation target, and divides the calculated area by a ratio of aneffective area, which is a ratio of the region Rc to the entire regionin which the slits Rs in the flow channel 13 are aligned. According tothis method, the counting of saturated slits, that is, the measurementof the amount of bacteria can be performed with high accuracy.

In the above embodiments, although an example of the inspection systemis described that the information processing device 21 constitutes thedisplay unit and the image analysis unit, the display unit and the imageanalysis unit may be configured separately. Further, the display unit orthe image analysis unit may be configured integrally with the inspectiondevice (dielectrophoresis device 1). Further, when the slits are countedvisually by the user, the image analysis unit may be omitted in theinspection system.

Summary of Aspects

As described above, 1st aspect according to the present invention is aninspection device (1) for inspecting an amount of dielectric particlescontained in a sample liquid. The inspection device includes adielectric collection unit (3), a pump unit (10) and an AC voltagesupply unit (11). The dielectric collection unit includes at least onepair of electrodes (41, 42) and a flow channel (13) extending in apredetermined direction on the pair of electrodes. The pump unit isconfigured to feed the sample liquid to follow the flow channel in thepredetermined direction. The AC voltage supply unit is configured tosupply, to the pair of electrodes, an AC voltage with a predeterminedfrequency to cause dielectrophoresis for dielectric particles in the fedsample liquid. The dielectric collection unit includes a plurality ofslit regions (Rs) aligned in the predetermined direction between thepair of electrodes. Each of the plurality of slit regions is separatedfrom each other within the flow channel.

2nd aspect according to the present invention is the inspection deviceof the 1st aspect, wherein a region in which the plurality of slitregions are connected to each other between the pair of electrodes isarranged outside the flow channel.

3rd aspect according to the present invention is the inspection deviceof the 1st or 2nd aspect, wherein the at least one pair of electrodesincludes a first electrode pair (CH1) and a second electrode pair (CH2)disposed on a downstream side of the first electrode pair in the flowchannel. The plurality of slit regions are famed between the secondelectrode pairs. The AC voltage supply unit supplies the AC voltage tothe first electrode pair and then supplies the AC voltage to the secondelectrode pair.

4th aspect according to the present invention is the inspection deviceof the 3rd aspect, wherein the AC voltage supply unit stops supply ofthe AC voltage to the first electrode pair, and while stopping supply ofthe AC voltage to the first electrode pair, the AC voltage supply unitsupplies the AC voltage to the second electrode pair.

5th aspect according to the present invention is the inspection deviceof the 3rd aspect, wherein the AC voltage supply unit changes afrequency of an AC voltage supplied to the first electrode pair, andwhile supplying an AC voltage with a changed frequency to the firstelectrode pair, the AC voltage supply unit supplies the AC voltage tothe second electrode pair.

6th aspect according to the present invention is the inspection deviceof any one of the 1st to 5th aspects, wherein the dielectric particlesinclude at least one of bacteria, cells, microorganisms, fungi, spores,and viruses.

7th aspect according to the present invention is the inspection deviceof any one of the 1st to 6th aspects further including the imaging unit(12) configured to capture an image of a predetermined region in whichthe plurality of slit regions are aligned in the dielectric collectionunit.

8th aspect according to the present invention is an inspection systemincluding the inspection device according to the 7th aspect and adisplay unit (21) configured to display an image captured by the imagingunit of the inspection device.

9th aspect according to the present invention is the inspection deviceof the 8th aspect further including an image analysis unit (21)configured to analyze an image captured by the imaging unit to countslits saturated with the dielectric particles.

10th aspect according to the present invention is the inspection deviceof the 9th aspect, wherein the sample liquid contains a fluorescentlabel causing the dielectric particles to emit fluorescence. The imageanalysis unit counts the saturated slits based on fluorescence emissionin the captured image.

11th aspect according to the present invention is the inspection deviceof the 9th or 10th aspect, wherein the image analysis unit applies anarea analysis method to the captured image to count the saturated slits.

12th aspect according to the present invention is an inspection methodfor inspecting an amount of dielectric particles contained in a sampleliquid. The method includes feeding the sample liquid to follow a flowchannel in a predetermined direction in a dielectric collection unit.The dielectric collection unit includes at least one pair of electrodes(41, 42) and the flow channel (13) extending in the predetermineddirection on the pair of electrodes. The method includes supplying, tothe pair of electrodes, an AC voltage with a predetermined frequency tocause dielectrophoresis for dielectric particles in the fed sampleliquid. The method includes counting slits saturated with the dielectricparticles among a plurality of slits aligned in the predetermineddirection between the pair of electrodes in the dielectric collectionunit.

13th aspect according to the present invention is the inspection methodof the 12th aspect, wherein the sample liquid contains a fluorescentlabel causing the dielectric particles to emit fluorescence. Thecounting is adapted to count slits that emit fluorescence as thesaturated slits.

14th aspect according to the present invention is the inspection methodof the 12th or 13th aspect, wherein the at least one pair of electrodesincludes a first electrode pair and a second electrode pair disposed ona downstream side of the first electrode pair in the flow channel. Thesupplying includes supplying the AC voltage to the first electrode pair,stopping supply of the AC voltage to the first electrode pair andsupplying the AC voltage to the second electrode pair. The counting isadapted to count the saturated slits in the second electrode pair.

15th aspect according to the present invention is the inspection methodof the 12th or 13th aspect, wherein the at least one pair of electrodesincludes a first electrode pair and a second electrode pair disposed ona downstream side of the first electrode pair in the flow channel. Thesupplying includes supplying the AC voltage to the first electrode pair,changing a frequency of an AC voltage supplied to the first electrodepair and supplying the AC voltage to the second electrode pair. Thecounting is adapted to count the saturated slits in the second electrodepair.

1. An inspection device for inspecting an amount of dielectric particlescontained in a sample liquid, the inspection device comprising: adielectric collection unit including at least one pair of electrodes anda flow channel extending in a predetermined direction on the pair ofelectrodes; a pump unit configured to feed the sample liquid to followthe flow channel in the predetermined direction; and an AC voltagesupply unit configured to supply, to the pair of electrodes, an ACvoltage with a predetermined frequency to cause dielectrophoresis fordielectric particles in the fed sample liquid, wherein the dielectriccollection unit includes a plurality of slit regions aligned in thepredetermined direction between the pair of electrodes, and wherein eachof the plurality of slit regions is separated from each other within theflow channel.
 2. The inspection device according to claim 1, wherein aregion in which the plurality of slit regions are connected to eachother between the pair of electrodes is arranged outside the flowchannel.
 3. The inspection device according to claim 1, wherein the atleast one pair of electrodes comprises a first electrode pair and asecond electrode pair disposed on a downstream side of the firstelectrode pair in the flow channel, wherein the plurality of slitregions are formed between the second electrode pairs, and wherein theAC voltage supply unit supplies the AC voltage to the first electrodepair and then supplies the AC voltage to the second electrode pair. 4.The inspection device according to claim 3, wherein the AC voltagesupply unit stops supply of the AC voltage to the first electrode pair,and while stopping supply of the AC voltage to the first electrode pair,the AC voltage supply unit supplies the AC voltage to the secondelectrode pair.
 5. The inspection device according to claim 3, whereinthe AC voltage supply unit changes a frequency of an AC voltage suppliedto the first electrode pair, and while supplying an AC voltage with achanged frequency to the first electrode pair, the AC voltage supplyunit supplies the AC voltage to the second electrode pair.
 6. Theinspection device according to claim 1, wherein the dielectric particlesinclude at least one of bacteria, cells, microorganisms, fungi, spores,and viruses.
 7. The inspection device according to claim 1, furthercomprising an imaging unit configured to capture an image of apredetermined region in which the plurality of slit regions are alignedin the dielectric collection unit.
 8. (canceled)
 9. (canceled)
 10. Theinspection system according to claim 16, wherein the sample liquidcontains a fluorescent label causing the dielectric particles to emitfluorescence, and wherein the image analysis unit counts the saturatedslits based on fluorescence emission in the captured image.
 11. Theinspection system according to claim 16, wherein the image analysis unitapplies an area analysis method to the captured image to count thesaturated slits.
 12. An inspection method for inspecting an amount ofdielectric particles contained in a sample liquid, the inspection methodcomprising: feeding the sample liquid to follow a flow channel in apredetermined direction in a dielectric collection unit, the dielectriccollection unit including at least one pair of electrodes and the flowchannel extending in the predetermined direction on the pair ofelectrodes; supplying, to the pair of electrodes, an AC voltage with apredetermined frequency to cause dielectrophoresis for dielectricparticles in the fed sample liquid; and counting slits saturated withthe dielectric particles among a plurality of slits aligned in thepredetermined direction between the pair of electrodes in the dielectriccollection unit.
 13. The inspection method according to claim 12,wherein the sample liquid contains a fluorescent label causing thedielectric particles to emit fluorescence, and wherein the counting isadapted to count slits that emit fluorescence as the saturated slits.14. The inspection method according to claim 12, wherein the at leastone pair of electrodes comprises a first electrode pair and a secondelectrode pair disposed on a downstream side of the first electrode pairin the flow channel, wherein the supplying comprises: supplying the ACvoltage to the first electrode pair; stopping supply of the AC voltageto the first electrode pair; and supplying the AC voltage to the secondelectrode pair, and wherein the counting is adapted to count thesaturated slits in the second electrode pair.
 15. The inspection methodaccording to claim 12, wherein the at least one pair of electrodescomprises a first electrode pair and a second electrode pair disposed ona downstream side of the first electrode pair in the flow channel,wherein the supplying comprises: supplying the AC voltage to the firstelectrode pair; changing a frequency of an AC voltage supplied to thefirst electrode pair; and supplying the AC voltage to the secondelectrode pair, and wherein the counting is adapted to count thesaturated slits in the second electrode pair.
 16. An inspection systemfor inspecting an amount of dielectric particles contained in a sampleliquid, the inspection device comprising: a dielectric collection unitincluding at least one pair of electrodes, a flow channel extending in apredetermined direction on the pair of electrodes, and a plurality ofslits aligned in the predetermined direction between the pair ofelectrodes; a pump unit configured to feed the sample liquid to followthe flow channel in the predetermined direction; an AC voltage supplyunit configured to supply, to the pair of electrodes, an AC voltage witha predetermined frequency to cause dielectrophoresis for dielectricparticles in the fed sample liquid, an imaging unit configured tocapture an image of a predetermined region in which the plurality ofslits are aligned in the dielectric collection unit; and an imageanalysis unit configured to analyze the image captured by the imagingunit to count slits saturated with the dielectric particles.
 17. Theinspection system according to claim 16, further comprising a displayunit configured to display the image captured by the imaging unit.